/*
 * Copyright 2007 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using ZXing.Common;
using ZXing.Common.ReedSolomon;

namespace ZXing.Datamatrix.Internal
{
   /// <summary>
   /// <p>The main class which implements Data Matrix Code decoding -- as opposed to locating and extracting
   /// the Data Matrix Code from an image.</p>
   ///
   /// <author>bbrown@google.com (Brian Brown)</author>
   /// </summary>
   public sealed class Decoder
   {
      private readonly ReedSolomonDecoder rsDecoder;

      /// <summary>
      /// Initializes a new instance of the <see cref="Decoder"/> class.
      /// </summary>
      public Decoder()
      {
         rsDecoder = new ReedSolomonDecoder(GenericGF.DATA_MATRIX_FIELD_256);
      }

      /// <summary>
      /// <p>Convenience method that can decode a Data Matrix Code represented as a 2D array of booleans.
      /// "true" is taken to mean a black module.</p>
      ///
      /// <param name="image">booleans representing white/black Data Matrix Code modules</param>
      /// <returns>text and bytes encoded within the Data Matrix Code</returns>
      /// <exception cref="FormatException">if the Data Matrix Code cannot be decoded</exception>
      /// <exception cref="ChecksumException">if error correction fails</exception>
      /// </summary>
      public DecoderResult decode(bool[][] image)
      {
         int dimension = image.Length;
         BitMatrix bits = new BitMatrix(dimension);
         for (int i = 0; i < dimension; i++)
         {
            for (int j = 0; j < dimension; j++)
            {
               if (image[i][j])
               {
                  bits[j, i] = true;
               }
            }
         }
         return decode(bits);
      }

      /// <summary>
      /// <p>Decodes a Data Matrix Code represented as a <see cref="BitMatrix" />. A 1 or "true" is taken
      /// to mean a black module.</p>
      /// </summary>
      /// <param name="bits">booleans representing white/black Data Matrix Code modules</param>
      /// <returns>text and bytes encoded within the Data Matrix Code</returns>
      public DecoderResult decode(BitMatrix bits)
      {
         // Construct a parser and read version, error-correction level
         BitMatrixParser parser = new BitMatrixParser(bits);
         if (parser.Version == null)
            return null;

         // Read codewords
         byte[] codewords = parser.readCodewords();
         if (codewords == null)
            return null;
         // Separate into data blocks
         DataBlock[] dataBlocks = DataBlock.getDataBlocks(codewords, parser.Version);

         int dataBlocksCount = dataBlocks.Length;

         // Count total number of data bytes
         int totalBytes = 0;
         foreach (var db in dataBlocks)
         {
            totalBytes += db.NumDataCodewords;
         }
         byte[] resultBytes = new byte[totalBytes];

         // Error-correct and copy data blocks together into a stream of bytes
         for (int j = 0; j < dataBlocksCount; j++)
         {
            DataBlock dataBlock = dataBlocks[j];
            byte[] codewordBytes = dataBlock.Codewords;
            int numDataCodewords = dataBlock.NumDataCodewords;
            if (!correctErrors(codewordBytes, numDataCodewords))
               return null;
            for (int i = 0; i < numDataCodewords; i++)
            {
               // De-interlace data blocks.
               resultBytes[i * dataBlocksCount + j] = codewordBytes[i];
            }
         }

         // Decode the contents of that stream of bytes
         return DecodedBitStreamParser.decode(resultBytes);
      }

      /// <summary>
      /// <p>Given data and error-correction codewords received, possibly corrupted by errors, attempts to
      /// correct the errors in-place using Reed-Solomon error correction.</p>
      ///
      /// <param name="codewordBytes">data and error correction codewords</param>
      /// <param name="numDataCodewords">number of codewords that are data bytes</param>
      /// </summary>
      private bool correctErrors(byte[] codewordBytes, int numDataCodewords)
      {
         int numCodewords = codewordBytes.Length;
         // First read into an array of ints
         int[] codewordsInts = new int[numCodewords];
         for (int i = 0; i < numCodewords; i++)
         {
            codewordsInts[i] = codewordBytes[i] & 0xFF;
         }
         int numECCodewords = codewordBytes.Length - numDataCodewords;
         if (!rsDecoder.decode(codewordsInts, numECCodewords))
            return false;

         // Copy back into array of bytes -- only need to worry about the bytes that were data
         // We don't care about errors in the error-correction codewords
         for (int i = 0; i < numDataCodewords; i++)
         {
            codewordBytes[i] = (byte)codewordsInts[i];
         }

         return true;
      }
   }
}
